1. Field of the Invention
This invention relates in general to computer disk drives, and more particularly to a method and apparatus for providing separate velocity profiles for read and write seeks.
2. Description of Related Art
In recent years microcomputer equipment such as personal or desk top computers have become extremely popular for a wide range of business, educational, recreational and other uses. Such computers typically include a main central processor having one or more memory storage disks for storage of data. The storage disk or disks are commonly provided as part of a so-called Winchester disk drive unit, sometimes referred to as a "hard" disk, wherein the storage disks are rotatably supported within a substantially sealed housing. The disks are rotatably driven in unison by a small spindle motor, and one or more electromagnetic heads are displaced by a head actuator assembly to traverse surfaces of the disks for purposes of reading and writing data. Such data is recorded onto magnetizable surfaces or surface films of the disks in the form of data bits located within narrow, closely spaced concentric tracks on the disks. Accordingly, for any given disk drive unit, the total memory storage capacity is directly proportional to the number of disks as well as the number of tracks on each disk.
In normal operations, a system controller of the main central processor has the capability to identify data stored by recording on the disks, typically through the use of directory name, file, name, and/or track address information. When reading of data at a specified data track is desired, the system controller displaces the head or heads to the desired position by supplying appropriate command signals to operate the head actuator assembly. Alternately, when data recording or writing is desired, the system controller operates the actuator assembly to align a selected head with a vacant data track. In either case, the head actuator assembly is commanded to displace the head or heads through a generally radial path relative to the disk for moving each head from alignment with a previously selected track to alignment with the newly selected destination track. Such movement of the head is normally referred to as a "seek" step.
Servo positioning systems have been widely employed for quickly and accurately positioning the mechanical element, such as a magnetic head of a magnetic recording disk apparatus. A typical servo control system for a recording disk apparatus includes a controller for generating a velocity signal based upon a position signal obtained from a servo signal generated by a magnetic head.
The position signal indicates the radial position of the magnetic head relative to the adjacent track and is generally designed to be zero when the head is at the center of a track being traced. The controller calculates the number of tracks needed to be jumped according to command from a host processor unit.
For optimum disk drive unit performance, it is desirable to displace the head or heads through each seek step in a minimum time period consistent with accurate head alignment with the destination track. Alternately stated, it is desirable to displace the head from one track to another at the fastest possible speed, including the fastest possible acceleration and deceleration without incurring a seek error.
However, the selection of a specific velocity profile during a seek step requires consideration of a wide range of electrical and mechanical design factors, some of which are subject to significant variations over time and/or from one computer to another. For example, temperature, mechanical stiffness of the actuator assembly, power supply voltage, etc. are subject to variations which can affect the optimum seek velocity profile without errors.
In the past, these design factors have been accommodated by selecting a seek velocity profile in accordance with a worst case condition, thereby minimizing or avoiding seek errors. Unfortunately, this approach results in a failure to utilize an optimized velocity profile for achieving minimum seek times during most normal operating conditions. For example, no distinction is made between read seeks and write seeks despite the fact that read seeks incur more errors that are induced by faster seek times, e.g., head positioning after seek.
There exists, therefore, a significant need for a relatively simple yet effective system for selecting a substantially optimized seek velocity profile of a disk drive unit.
It can be seen then that there is a need for a computer disk drive unit having a control system that uses a separate velocity profile for read seeks and for write seeks.
It can also be seen that there is a need for a control system having a write seek velocity profile that reduces random transient vibrations.
It can also be seen that there is a need for a control system having a more aggressive read seek profile since random transient vibrations and settle time are not critical.